Microbiology Lecture Notes PDF

Gram +ve Cocci STAPHLOCOCCUS  Introduction Gram positive cocci (0.5-1.5 mm) ) Occur in grape like clusters (in singles, in pairs) In Greek staphyle - Bunch of grapes Kokkus- Berry Include major human pathogen and skin commensals Micrococcus- skin commensal o S. aure...

Gram +ve Cocci STAPHLOCOCCUS  Introduction Gram positive cocci (0.5-1.5 mm) ) Occur in grape like clusters (in singles, in pairs) In Greek staphyle - Bunch of grapes Kokkus- Berry Include major human pathogen and skin commensals Micrococcus- skin commensal o S. aureus ( most important ) o S. epidermidis o S. saprophyticus  Classifications B) Based on pathogenicity: A) Based on coagulase production: 1. Common pathogen: S. aureus 1. Coagulase positive: S. aureus 2. Opportunistic pathogens: 2. Coagulase negative: S. epidermidis S. epidermidis S.saprophyticus S. saprophyticus 3. Non pathogen: S. homonis Culture characteristics 1. On nutrient agar ; golden yellow pigment 2. On MacConkey’s agar ; Pink in color 3. On blood agar ; β- hemolytic colonies.  Staph aureus Toxins Characteristics:- Enterotoxin Usual sites - skin, nasopharynx, perineum Toxic shock syndrome toxin Produce superficial to systemic infections (PUS) Structure and virulence factors Exfoliatin Protein A Haemolysins Catalase (counters host defenses) Leucocidin (Panton- Coagulase (virulence marker) Valentine toxin) Hyaluronidase (spread of infection) Lipases (allows colonization) B lactamase (antibiotic resistance) DNase (degrades DNA) Teichoic acids Polysaccharide capsule Peptidoglycan PATHOGENICITY: SOURCE OF INFECTION: A) EXOGENOUS: PATIENTS OR CARRIERS B) ENDOGENOUS: FROM COLONIZED SITE MODE OF TRANSMISSION: A) CONTACT: DIRECT OR INDIRECT (THROUGH FOMITES) B) INHALATION OF AIR BORNE DROPLETS  Disease caused by S.aureus  Infection Folliculitis  Intoxication – Food poisoning – Toxic shock syndrome – Staphylococcal scalded skin syndrome  Treatment Drain infected area Deep/metastatic infections semi-synthetic penicillin's cephalosporin's erythromycin clindamycin Endocarditis semi-synthetic penicillin + an aminoglycoside MRSA Infection start out small red bumps that can quickly turn into painful abscesses  VISA AND VRSA Vancomycin is the drug of choice for treating MRSA infections Staphylococcus aureus with decreased (intermediate ) susceptibility to vancomycin = VISA Staphylococcus aureus with resistance genes Van A or Van B = VRSA So far only few isolates in different parts of the world  Staphylococcus Staphylococcus Epidermis Saprophyticus It has predilection for growth on implanted foreign bodies Men are infected much such as artificial valves, shunts, less often. intravascular catheters and prosthetic appliances leading It is one of the few to bacteraemia. frequently isolated CoNS that is resistant to In persons with structural Novobiocin. abnormalities of urinary tract, it can cause cystitis DIFFERENCES S. Epidermis S. Saprophyticus Coagulase Test Negative Negative Pathogenicity Opportunistic Opportunistic Novobiocin Sensitive Resistant 1. Skin/wound infections 1. Peritonitis 2. Endocarditis 2. Enopthalmitis 3. UTI 3. Endocaritis 4. UTI/cystitis Phosphatase Positive Negative Acid from mannitol Negative Negative fermentation anaerobically Teichoic acid, Protein A, Absent Absent Β-hemolysis, Pigment Predisposing Factors Failure to follow asceptic Sexual activity procedure Streptococcus LAB DIAGNOSIS OF GAS  STEPS OF DIAGNOSIS: Collection of specimen Microscopic examination Inoculation of culture media Biochemical test Agglutination test Serological diagnosis Antimicrobial susceptibility tests  Bacitracin Sensitive Test To determine the effect of bacitracin on organism. GAS is inhibited by small amount of bacitracin in the disk other beta-hemolytic streptococci usually are not. Positive test for Group A.  Rapid strep test It is a rapid antigen detection test (RADT) For diagnosis of bacterial pharyngitis caused by group A streptococci (GAS) Sometimes termed as strep throat.  ASLO Test Serological diagnosis To detect anti-streptolysin O antibodies in patient serum SLO is present in streptococci of Group A  Topic: Lab diagnosis of GBS(Group B Streptococcus)  Introduction: Streptococcus agalactiae, also known as Group B streptococcus (GBS) Gram-positive colonizing bacterium Cause serious disease in newborns  Differential Diagnosis Beta hemolytic Catalase negative Bacitracin resistant CAMP factor  CAMP Reaction CAMP + strain of S.aureous Positive control group B Negative control group A Unknown strep translucent on SB Sheep blood agar plate  Bacitracin Test Antibiotic No zone of inhibition Bacitracin resistant PYR Test Enzyme in pyogenes Test positive  Group D streptococci Group D streptococci include Enterococci (e.g., E. faecalis and Enterococcus faecium) Nonenterococci (e.g., S. bovis).  Diseases Enterococcus faecalis is an important cause of hospital-acquired urinary tract infections and endocarditis.Predisposing factors are: Foley’s catheter and gut or bladder surgery or instrumentation Streptococcus bovis also causes endocarditis. Predisposing factor is Colon CA.  Group D streptococci Enterococcus Non- Enterococcus Cause of UTI and endocarditis Cause of UTI and very hardy organisms endocarditis they can grow in hypertonic (6.5%) saline or in bile much less hardy organisms are not killed by penicillin G they are inhibited by 6.5% Treatment choices: NaCl 1. synergistic combination of penicillin & a aminoglycoside killed by penicillin G. 2. Vancomycin is another drug to treat VRE have emerged. (More strains of E. faecium are vancomycin resistant than are strains of E. faecalis)  Pneumococcus Infections Bacterial Infection (streptococcus pneumoniae) Types Invasive Infection Non Invasive Infections  Streptococcus pneumoniae Pathology – Pneumonia – Meningitis – Sepsis – Otilis media (in children) Treatment – Penicillin G – Erythromycin – Ceftriaxone – Vaccine: made against 23 most common capsular antigens.  Lab Diagnosis of PNEUMOCOCCUS Gram Stain Test Gram staining is a common technique used to differentiate two large groups of bacteria based on their different cell wall constituents. Streptococcus pneumoniae is a gram-positive coccus. Usually they are found in of cocci, or diplococci may also occur in short chains or singly. When cultured on blood agar they demonstrate alpha hemolysis. They are non motile organisms. Lab Diagnosis of PNEUMOCOCCUS Optochin test Optochin susceptible Optochin resistant (≥14 (